Brass or gun metal clamps may be kept clean by brushing them over with melted paraffin after they have been screwed up tightly. When thus treated they serve to indicate points of bad contact by heat, generated at such points, when the current is flowing, softening the paraffin and changing its normal color. Vaseline and different kinds of anti-sulphuric acid varnishes, or preparations that are not attacked by the electrolyte, may also be used for this purpose. It is a good plan to color the varnish with vermillion or lamp black and paint the positive connections red and the negative connections black, and also other parts of the installation for distinguishing the polarities.
=Cell Connections.=—The cells may be connected together either in series or parallel, or in parallel-series or series-parallel combinations, according to the requirements, but in all cases it is best to use the simplest arrangement practicable.
For instance: if the cells employed in an installation requiring 110 volts, have only half the capacity required, and 55 cells give the desired voltage, then the number of cells must be increased to 110, and theoretically the required number of amperes hours at 110 volts may be obtained in one of two ways: 1, by connecting the cells in pairs in parallel and then coupling the pairs together in series, and 2, by arranging the 110 cells in two complete batteries of 55 cells each connected in series, then coupling the two batteries in parallel.
The first method is quite impracticable, however, as the slightest difference between the voltages of the two cells of any pair will result in the one having the greater pressure discharging into the other, thereby causing the entire battery to quickly deteriorate.
NOTE.—_To determine the positive wire._ Without a voltmeter, the positive terminal of the charging circuit can be determined by attaching a piece of clean lead to each wire which is to be connected to the battery, and immersing them, without touching each other, in a glass or other insulating vessel containing water to which is added a drop or two of sulphuric acid. After the current has passed through the circuit for a short time, the positive lead will commence to discolor, and, if left long enough, will turn brown. Bubbles will arise from the two terminals immersed, the larger and more frequent ones being from the negative, the smaller ones from the positive.